(1) Field of the Invention
The present invention relates to a disk track emulation system and method, and in more detail, to a disk track emulation system and method used in a disk system in a computer system (hereinafter, a system including a disk device and a disk control device is referred to as a disk system). In particular, the present invention relates to a disk track emulation system and method capable of maintaining a compatibility between the data format of a conventional system and the data format of a new system when the disk system is replaced by a system with a disk track having a different data format.
(2) Description of the Related Art
For users who are using a conventional disk system, when the disk system is replaced with a higher capacity device, problems such as data compatibility or transfers between the conventional device and the new device become serious.
An important factor in data compatibility or transfer is a track capacity or data transfer speed. Namely, the track capacity or the data transfer speed of the conventional system and the new system may be different.
Recent technological developments have led to a large capacity disk device (such as a magnetic disk device), and inevitably, the capacity per one track has been increased, and further, in new disk devices, the data transfer speed has been increased. Therefore, when the disk devices are replaced, due to the above-mentioned differences in the capacities or the data transfer speeds, the data formats on tracks of the new device and the conventional device may be different, and in such a case, it is impossible to maintain the data compatibility.
Therefore, to meet the needs of users, it has become important to be able to emulate a data format of a conventional disk device on a new disk device. The emulation may be accomplished with a system and method of providing a compatibility (disk track emulation) of a disk track format (data format) of a new device with that of a disk track format (data format) of a conventional device.
Namely, when a conventional disk system including a disk control device and a disk device is replaced by a new disk system, and when the track capacity and the data transfer speed of the new disk system are greater than those of the conventional disk system, obviously, the data formats of disk tracks of the conventional disk system and the new disk system are different. For example, due to the different track capacities, the total track of the conventional disk system is divided into 1554 cells, where each cell has 32 bytes. In the new disk system however, the total track is divided into 1944 cells, each having 34 bytes.
Also, to improve the data transfer speed, the new disk system has a higher disk rotating speed and a different number of cells in a gap between an index mark and a home address, and between the home address and a count area, etc., in comparison with those of the conventional disk system.
When such a new disk system is connected to a conventional host device, the data format of the conventional disk track cannot be used as it is, because it is different from that of the new disk track.
Therefore, conventionally, to connect the new disk system to the host device so as to be workable, it is necessary to prepare a new data conversion program or to reform the user program and so forth used in the host device into a program suitable for the new disk system.
In the above-described conventional art, the following problems exist.
(a) To replace a conventional disk system with a new disk system having a disk track with a different data format, and to work by connecting the new disk system to a host device, the user must prepare a new program for working the new disk system. This preparation of a program, however, takes much time and labor.
Accordingly, if the data format of the disk track is modified, the preparation of a program at each time of modification is time-and labor consuming.
(b) When a conventional disk device is replaced by a new disk device having a disk track with a different data format, no problem arises if the host device is replaced along with the conventional disk system, but this is wasteful of the resources of the user.
(c) When a conventional disk system including a conventional disk device and a conventional disk control device is replaced by a new disk system including a new disk device and having a disk track with a different data format, and when the new disk control device is connected to a host device to operate the new disk system, ideally the program for the host device need not be reformed and the program can be used as if it is used for the conventional disk system, and thus the above-mentioned problems (a) and (b) do not arise.
To realize such a system, however, the following problems must be resolved, and therefore, it has not been conventionally realized.
Namely, when the host device is maintained as the conventional host device, and when the disk control device and the disk device are replaced by a new disk system as mentioned above, it is necessary to carry out the following data processing to operate the new disk system without reforming the program of the host device.
The data transfer between the disk control device and the disk device is controlled under the new data format, but between the disk control device and the host device, it must be controlled under the conventional data format.
Consequently, the data transfer from the host device to the disk control device, and the data transfer from the disk control device to the host device must be carried out in accordance with the conventional data format whereby, from the host device, the new disk system performs as if carrying out the data processing by the conventional data format.
To this end, it is necessary to perform various converting processes in the disk control device, but these converting processes have two problems to be solved.
(a) To realize a compatibility between the host device and the disk control device, the physical record position data, called the cell numbers CN respectively recorded on the records written on the track of the new data format, must be the same values as those in the conventional data format. When the disk control device controls the disk device by the physical track positions, to perform a process such as a skipping of a damaged position on the track, real position data is necessary, but since the data formats are different, it is impossible for the host device to know the real position data in the new disk device without reforming the program.
(b) The total track capacities of the conventional disk system and the new disk system are different. For example, the track capacity of the conventional disk system is 1554 cells, each cell having 32 bytes, whereas the track capacity of the new disk system is 1944 cells, each cell having 34 bytes.
Also, the intervals between records referred to as gaps of the conventional system and the new system are different, and therefore, when data is written up to the physical limit of, for example, 1944 cells, for writing in the new track, it becomes over written in the conventional system and exceeds the limit for writing in accordance with the conventional data format.
Accordingly, data must not be written up to the physical limit for writing in the new track, and the limit for writing must be detected before the data is written up to the physical limit for writing in accordance with the conventional data format.